This invention relates to the recovery of nickel and copper from concentrates which contain minerals of both metals.
The specification of South African patent No. 98/2549 describes a process for the recovery of copper which includes the following steps:
(a) biologically oxidising copper sulphate concentrate in slurry form to dissolve copper as soluble copper sulphate;
(b) subjecting the slurry to solid/liquid separation to produce a solution with a high copper concentration;
(c) treating the solution with a solvent extraction reagent so that copper ions are exchanged by the reagent for hydrogen ions to produce a raffinate which is high in sulphuric acid and low in copper sulphate;
(d) stripping the solvent extraction reagent with a sulphuric acid solution;
(e) electrowinning copper from the sulphuric acid solution; and
(f) using at least a portion of the raffinate from step (c) in step (a).
An important feature of this process is the application of biologically assisted leaching of copper concentrates with the use of a portion of the raffinate produced by solvent extraction to satisfy the demand for acid in the leaching step.
The present invention is concerned with the recovery of nickel and copper from a concentrate which contains a substantial amount of nickel.
The invention provides a process for recovering nickel and copper from a concentrate which includes the steps of:
(a) subjecting the concentrate to a treatment phase to produce:
(1) a first leach solution which contains predominantly copper and
(2) a second leach solution which contains predominantly nickel;
(b) subjecting the first leach solution to a process for copper recovery which includes a solvent extraction step to produce a raffinate which is high in sulphuric acid;
(c) recycling at least a portion of the raffinate to the treatment phase of step (a), and
(d) subjecting the second leach solution to a process for nickel recovery.
In one form of the invention the treatment phase of step (a) includes the steps of:
(e) separating the concentrate by flotation into a first concentrate which is substantially a copper concentrate and a second concentrate which is substantially a nickel concentrate;
(f) biologically oxidising the first concentrate to produce the said first leach solution, and
(g) biologically oxidising the second concentrate to produce the said second leach solution.
With this form of the invention the raffinate produced in step (b) is recycled at least to the oxidation step (f). The raffinate may, depending on the conditions, also be recycled to the oxidation step (g).
The process of step (d) may include a step of solvent extraction to extract copper from the second leach solution before nickel is recovered from the second leach solution.
Preferably step (f) is carried out at an elevated temperature, eg. from 65xc2x0 C. to 80xc2x0 C., so that thermophilic archaea such as Sulfolobus are active and chalcopyrite is thereby dissolved by biological oxidation.
In a second form of the invention the treatment phase of step (a) includes the steps of subjecting the concentrate in series:
(h) to a first biological oxidation step to dissolve nickel as nickel sulphate in the said second leach liquor, and
(i) to a second biological oxidation step to dissolve copper as copper sulphate in the said first leach liquor.
In step (h) the oxidation may be conducted at a moderate temperature, of the order of from 40xc2x0 C. to 45xc2x0 C., to dissolve pentlandite as nickel sulphate, with use being made of mesophilic, or moderate thermotolerant, bacteria.
In step (i) the oxidation may be conducted at a relatively elevated temperature, of the order of 70xc2x0 C. to 80xc2x0 C., to dissolve chalcopyrite as copper sulphate, with use being made of thermotolerant or thermophilic bacteria or archaea, such as the type Sulfolobus.
In each case solid/liquid separation is used to obtain a solution.
The nickel sulphate may be subjected to solvent extraction for copper, before nickel recovery takes place.
The copper sulphate is subjected to solvent extraction for copper, thereby producing the said raffinate which is high in sulphuric acid and which is recycled to at least one of the oxidation steps.